Smart Secure Electricity Systems (SSES) tariff interoperability: code and licence modifications

DESNZ·decision·HIGH·18 May 2026·Updated 18 May 2026·source document

Summary

The Secretary of State has used Energy Act 2023 section 245(1)(a) and (e) powers to insert new Standard Licence Condition 11C into the Electricity Supply Licence and a new Schedule 35 into the Retail Energy Code, mandating that electricity suppliers expose tariff and export-tariff pricing data via a standardised API. The licence condition takes legal effect on 18 February 2027; suppliers must build a compliant Tariff Interoperability API, register a Supplier Endpoint with RECCo by 31 December 2026, and meet 99.9% monthly availability with a 95th-percentile 1-second response time at steady-state volume. Smaller non-domestic-only suppliers below 100,000 meter points are exempt, as are block tariffs, current-transformer-metered sites, and bespoke charges.

Why it matters

This forces suppliers to make machine-readable price signals a regulated public utility so that EV chargers, heat pumps and other smart appliances can shop tariffs automatically; it lowers the transaction cost of switching consumption to cheap periods, which is the precondition for consumer-led flexibility to actually discipline demand rather than remain a planning aspiration. The cost falls on suppliers (API build, 99.9% uptime, monthly performance reporting to RECCo) and the de minimis carve-out at 100,000 non-domestic meter points tilts the burden toward incumbents while sparing the smallest entrants; the structural risk is that the value of automated tariff-shopping is capped by how genuinely cost-reflective and time-varying the underlying tariffs are, which this instrument does not touch.

Key facts

•New Electricity Supply Standard Licence Condition 11C inserted after Condition 11B; new REC Schedule 35 (v1.0) and Schedule 1 definitions inserted
•Made under Energy Act 2023 s.245(1)(a) (licence modification) and s.245(1)(e) (code modification) for the purpose of regulating load control
•Code/licence text modifications take effect 18 May 2026; substantive duty (Condition 11C.2) and REC Paragraphs 2-3 apply from 18 February 2027 (go-live)
•Each TI Energy Supplier must provide its Supplier Endpoint to RECCo by 31 December 2026
•De minimis exemption: non-domestic-only suppliers with no more than 100,000 Relevant TI Non-Domestic Premises (by meter points), or supplying only deemed/out-of-contract customers
•Carve-outs: block/volume-varying tariffs, current-transformer-metered (Excepted Customer) sites, unmetered supply, bespoke charges incompatible with technical requirements
•Non-functional requirements: 99.9% monthly API availability; 95th-percentile response 1s at steady state (1,000 req/s), 5s at peak (5,000 req/s for any 5-min window); rate limits 10,000 req/s total and 1,000 req/s per IP
•Amended tariff data must be available via the API at least 60 minutes before a price change takes effect
•15-month data retention (3 months live, remainder archived); retry strategy of 3 attempts at 20s then hourly with 12-hour buffer
•Gas suppliers and non-mandated electricity suppliers may opt in voluntarily (3 months' notice to cease); RECCo maintains a public TI Supplier Register
•Government response to the 2025 Tariff Interoperability consultation published 11 May 2026 on the REC website; signed by Funmi Brady, DESNZ, 13 May 2026

Timeline

Effective date18 May 2026

Areas affected

retail marketflexibilitybehind the metersuppliersstorage

Related programmes

Energy Act 2023MHHSNet Zero

Memo

What changed

The Secretary of State has used the load-control modification powers in section 245(1)(a) and (e) of the Energy Act 2023 to insert a new Standard Licence Condition 11C into the Electricity Supply Licence and a new Schedule 35 into the Retail Energy Code. Both modifications were signed by DESNZ on 13 May 2026 and take legal effect on 18 May 2026, following the government response to the 2025 Tariff Interoperability consultation published on 11 May. This is the first delivery phase of the Smart Secure Electricity Systems programme.

The substance is a duty on electricity suppliers to expose their pricing in a machine-readable form. Condition 11C requires licensees to make available their Charges for the Supply of Electricity and their Export Tariffs via a standardised Tariff Interoperability API, governed by detailed Retail Energy Code requirements administered by RECCo. The operative date for the licence duty is deferred to 18 February 2027; the intervening period is build-and-test time. The decision does not set the tariffs, touch their structure, or require them to be time-varying. It regulates only the pipe through which prices are published.

What this means in practice

Every domestic electricity supplier is in scope, plus any gas supplier that opts in. The carve-out is narrow and deliberate: a supplier escapes the duty only if it has never previously been caught by it, supplies non-domestic customers only, and either serves no more than 100,000 non-domestic meter points across the group or would only ever be publishing deemed and out-of-contract prices. Three further structural exclusions apply regardless of size: block tariffs (where the unit rate or standing charge varies with consumption volume in a period), current-transformer-metered sites, and bespoke charges tailored to a single customer. Unmetered supplies are out.

The compliance burden is concrete and largely fixed-cost. Each supplier must build a TI API to RECCo's technical specification, register a Supplier Endpoint with RECCo by 31 December 2026, and from go-live meet a service level that is genuinely demanding for a price-publishing system: 99.9% availability measured monthly, a 95th-percentile response time of 1 second at steady-state volume (at least 1,000 requests per second of capacity), 5 seconds up to peak (5,000 requests per second for any five-minute window), rate limits at 10,000 requests per second overall and 1,000 per IP, a 12-hour message buffer with a defined three-retries-then-hourly strategy, 15 months of data retention, and a monthly performance report to RECCo. Amended prices must be visible on the API at least 60 minutes before they take effect. RECCo itself bears the Supplier Register and audit infrastructure cost, recovered through REC charges, so the central cost is socialised across all REC parties while the API cost sits with each supplier individually.

This is a fixed-cost compliance obligation laid on top of a flat exemption threshold, which is the standard shape of an instrument that favours incumbents. A large supplier amortises the API build and the uptime engineering across millions of meter points; a small domestic entrant pays substantially the same absolute cost across far fewer. The 100,000-meter-point relief does nothing for that entrant because it is restricted to non-domestic-only suppliers. The barrier-to-entry effect is real, though modest relative to the rest of the supply licence, and the standardised specification at least prevents each supplier inventing its own interface.

The economic logic of the instrument is sound as far as it goes. Consumer-led flexibility has been a planning aspiration for years precisely because the transaction cost of acting on a price signal is prohibitive for a household: nobody reschedules their EV charging by reading a tariff sheet. Making the price signal machine-readable and queryable lets an EV charger or heat pump shop tariffs and shift load automatically, which is what turns flexibility from a modelled assumption into a behaviour that actually disciplines demand. The standard is being made a regulated public utility because the market did not produce it voluntarily, which is a reasonable diagnosis of a coordination failure.

The limit is structural and unaddressed. Automated tariff-shopping is only worth as much as the underlying tariffs are cost-reflective and time-varying. If most domestic tariffs remain flat or weakly differentiated, a perfectly engineered API surfaces prices that give appliances little to optimise against. This instrument builds the rails; it does not change what runs on them. The value case depends on a separate movement toward dynamic, locationally and temporally granular pricing that nothing here mandates.

What happens next

The binding milestones are sequential: Supplier Endpoint registration with RECCo by 31 December 2026, then the licence duty and the operative parts of Schedule 35 (Paragraphs 2 and 3) commencing on 18 February 2027, with the Secretary of State retaining power to designate a later go-live date. Before go-live, suppliers build against a transition version of the TI API Technical Specification that RECCo maintains in consultation with DESNZ; that specification is folded into the REC by amendment in due course, and RECCo may require participation in pre-go-live testing.

Several pieces are not yet fixed. The TI API Technical Specification is a Category 3 REC product still being finalised, as are the Data Specification, the Performance Assurance Report Catalogue, and the consumer-consent and data-security requirements listed but not detailed in Condition 11C's Retail Energy Code Requirements definition. Ofgem holds a derogation power under 11C.8 to relieve individual suppliers, on consultation, for a specified period and on specified conditions. Watch for the gas-supplier opt-in take-up, the eventual treatment of the structural carve-outs (block tariffs and CT-metered sites are excluded now but are exactly where some flexible non-domestic load sits), and whether a later phase pairs the interoperability rail with any move toward more cost-reflective tariffs, without which the consumer-saving rationale stays largely theoretical.

Source text4,538 words

The Smart Secure Electricity Systems ( SSES ) Programme is designed to create the technical and regulatory frameworks to unlock the untapped flexibility from small scale devices, such as domestic electric vehicle charge points and heat pumps. The Tariff Interoperability Arrangements will introduce an obligation on electricity suppliers to make pricing data available in a standardised format. This is an important government-led initiative which will make it easier for electricity customers to participate in consumer-led flexibility by automating how Energy Smart Appliances ( ESAs ) connect to price signals. This will enable consumers to save money on their electricity bills. The initial phase of Tariff Interoperability will be delivered by introducing changes to the Electricity Supply Standard Licence Conditions and the Retail Energy Code. Section 245(1)(a) of the Energy Act 2023 gives the Secretary of State power to make modifications to licences, and section 245(1)(e) provides power to modify the industry codes maintained in accordance with the conditions of these licences for the purposes of facilitating, promoting, ensuring the security of, or otherwise regulating load control. In accordance with section 246(1) of the Energy Act 2023, we have consulted on Tariff Interoperability proposals in the 2024 Delivering a Smart Secure Electricity System consultation, and most recently conducted the 2025 Tariff Interoperability consultation in collaboration with the Retail Energy Code Company ( RECCo ). We have now published the government response to the 2025 Tariff Interoperability consultation on the Retail Energy Code website. Taking responses into account, the Secretary of State has made a modification to the Electricity Supply Standard Licence Conditions and the Retail Energy Code as set out in the Decision Notice. The modification sets out the requirements for how electricity suppliers must share tariff data. The modifications, as set out in the Decision Notice, will take effect from 18 May 2026. ENERGY ELECTRICITY NOTICE OF MODIFICATION OF THE ELECTRICITY SUPPLY STANDARD LICENCE CONDITIONS AND THE RETAIL ENERGY CODE The Secretary of State modifies the Electricity Supply Standard Licence Conditions and the Retail Energy Code as set out in this notice in exercise of the power conferred by section 245(1)(a) and (e) of the Energy Act 2023 (“the Act”). In this notice “Electricity Supply Standard Licence Conditions” means licence granted under Section 6 (1) (d) of the Electricity Act 1989 and “Retail Energy Code” means the document maintained in accordance with Condition 11B of the Electricity Supply Standard Licence Conditions. The Secretary of State in collaboration with the Retail Energy Code Company (RECCo) consulted in Winter 2025 on proposed modifications of the Electricity Supply Standard Licence Conditions and the Retail Energy Code in connection with Tariff Interoperability for the Smart Secure Electricity Systems Programme, and on 11th May 2026 published a response to that consultation. On the basis of the conclusions in that response to consultation, the Secretary of State decides, with effect from 18th May 2026, to make the following changes: Modifications to the Electricity Supply Standard Licence Conditions 1. The Electricity Supply Standard Licence Conditions are modified in accordance with paragraph 2 with effect from 18 May 2026. 2. After ‘Condition 11B. Retail Energy Code’ insert new condition 11C as follows: “Condition 11C. Making available information related to Charges for the Supply of Electricity and Export Tariffs PART A. APPLICATION 11C.1 This condition shall have effect from 18 February 2027. PART B. THE DUTY TO MAKE AVAILABLE INFORMATION 11C.2 Subject to paragraph 11C.3, the licensee must make available information related to its Charges for the Supply of Electricity (excluding any charges for the provision of an Electricity Meter) to Domestic Premises and Relevant TI Non- Domestic Premises and Export Tariffs in accordance with the Retail Energy Code Requirements as modified from time to time. 11C.3 Paragraph 11C.2 does not apply to the licensee if: a) neither the licensee nor any Affiliate has previously been required to meet the requirements of paragraph 11C.2; and b) the licensee supplies electricity only to Non-Domestic Customers; and either (i) the licensee in conjunction with its Affiliates supplies electricity to no more than 100,000 Relevant TI Non-Domestic Premises based on number of meter points; or (ii) the only information that the licensee would be required to make available under this condition is information that pertains to Deemed Contracts and/or Out-of-contract Contracts. 11C.4 The licensee must take all reasonable steps to ensure that the information made available in accordance with paragraph 11C.2 is: a) subject to paragraphs 11C.5 and 11C.6, made available in relation to the Charges for the Supply of Electricity and Export Tariffs applying at all Domestic Premises and Relevant TI Non-Domestic Premises; b) complete, in that all data fields required by the Retail Energy Code Requirements in relation to the Charges for the Supply of Electricity and Export Tariffs at any particular premises are populated; and c) accurate and up to date. 11C.5 The licensee shall not be required to make available the information in accordance with paragraph 11C.2 to the extent that the Charges for the Supply of Electricity applying in relation to a particular premises: a) are structured in a manner that is incompatible with technical requirements imposed by the Retail Energy Code Requirements; b) are such that the Unit Rate or Standing Charge applying in any period varies depending on the quantity of electricity consumed within that period; or c) apply to an Unmetered Supply. 11C.6 The licensee shall not be required to make available the information in accordance with paragraph 11C.2 in relation to a Relevant TI Non-Domestic Premises: a) that is occupied by an Excepted Customer; or b) to the extent that the information relates to Bespoke Charges. 11C.7 The licensee must keep a record of, and make available on request to the Secretary of State or to the Authority in a form and manner stipulated by the Secretary of State or the Authority (as the case may be) the following information: a) the number of times third parties have, in accordance with the Retail Energy Code Requirements, accessed the information related to the licensee’s Charges for the Supply of Electricity or Export Tariffs; and b) the structure of any Charges for the Supply of Electricity or Export Tariffs that it does not make available in accordance with the requirements of 11C.2 by virtue of paragraph 11C.5. c) in either case in relation to any time period specified by the Secretary of State or the Authority (as the case may be). 11C.8 The Authority may, following consultation with the licensee and where appropriate any other person likely to be materially affected, give a direction (“a derogation”) to the licensee that relieves it of its obligations under paragraph 11C.2, to such extent, for such period of time and subject to such conditions as may be specified in the direction. 11C.8 Definitions For the purposes of this condition: Bespoke Charges means Charges for the Supply of Electricity that are tailored to the individual needs of a Customer being supplied by the licensee and that are not widely available on the open market, but excluding Charges for the Supply of Electricity that would otherwise be treated as Bespoke Charge solely because of the inclusion of a fee that is paid (either directly or indirectly) to a Micro Business TPI. Excepted Customer means a customer that the licensee supplies at one or more premises at which the quantity of electricity supplied to the premises is determined by a Current Transformer Electricity Meter. Export Tariff means, as between the licensee and a Customer, payments and/or charges made by the licensee in respect of the generation or export of electricity at or from that Customer’s premises, including (but not limited to) the unit price for the purchase of exported or generated electricity and any other related unit or standing prices and/or charges and including payments and/or charges made based on either measured or estimated quantities of generation or export of electricity, but excluding any charges for the provision of Metering Equipment. Micro Business TPI has the meaning given to that term in standard condition 7D. Out-of-contract Contract has the meaning given to that term in standard condition 7A. Relevant TI Non-Domestic Premises means a Non-Domestic Premises at which the quantity of electricity supplied to the premises is not determined by a Current Transformer Electricity Meter. Retail Energy Code Requirements means the requirements specified in the Retail Energy Code for the purposes of this condition that set out: a) the data items relating to Charges for the Supply and Export Tariffs of Electricity that are to be made available; b) the ancillary information that must or may also be made available; c) the mechanism and format by which those data items and ancillary information must be made available; d) the means by which a record may be established of the extent to which the information related to the licensee’s Charges for the Supply of Electricity and Export Tariffs has been accessed by third parties; e) in respect of the systems used by the licensee to make information available, the performance requirements that must be met; f) the persons to whom the information must be made available and the circumstances in which it must be made available to those persons; g) the arrangements by which those accessing the information can have a reasonable degree of confidence that the information being provided is genuine; h) matters relating to consumer consent and data protection and security, including user requirements when accessing information made available and suspension and revocation of access; and i) any other associated or ancillary matters. Unmetered Supply has the meaning given to that term in condition 22E.7.” Modifications to the Retail Energy Code – Interpretations and Definitions Schedule and Tariff Interoperability Arrangements Schedule 3. The Retail Energy Code is modified in accordance with paragraph 4 and 5 with effect from 18 May 2026. 4. In Schedule 1 - Interpretations and Definitions Schedule, paragraph 3.1 - a) after the term “Supplier Agent” insert a new definition as follows: “ Supplier Endpoint means a URL address provided by a Tariff Interoperability Energy Supplier for receiving Tariff Interoperability API requests. “ b) after the term “Tariff Code” insert new definitions as follows: “ Tariff Identifier Tariff Id means a TI Energy Supplier specific identifier, required to identify each unique set of Tariff Pricing Data e.g. the standing charge and unit rate applicable where relevant factors are combined such as payment method or location. Tariff Interoperability API Technical Specification means the Category 3 Product of that name that describes the specification for Tariff Interoperability APIs and other technical requirements. Tariff Interoperability Application Programming Interface (API) TI API means any application programming interface defined within the TI API Technical Specification. Tariff Interoperability Arrangements means the arrangements described in the Tariff Interoperability Arrangements Schedule to facilitate the sharing of Tariff Pricing Data in accordance with the Tariff Interoperability Licence Condition. Tariff Interoperability Energy Supplier TI Energy Supplier means either: (a) an Electricity Supplier which is required by its Energy Supply Licence to provide Tariff Pricing Data under the Tariff Interoperability Arrangements; or (b) an Energy Supplier which is not required by its Energy Supply Licence to provide Tariff Pricing Data but has: (i) notified its intention to participate in the Tariff Interoperability Arrangements in accordance with Paragraph 1.7 of the Tariff Interoperability Arrangements Schedule; and (ii) not given notice to cease participating in the Tariff Interoperability Arrangements in accordance with Paragraph 1.8 of the Tariff Interoperability Arrangements Schedule. Tariff Interoperability Licence Condition means Condition 11C (Making available information related to Charges for the Supply of Electricity and Export Tariffs) of the Electricity Supply Licence. Tariff Interoperability Market Messages means the Market Messages used to request and share Tariff Pricing Data, as defined within the Data Specification. For the purpose of this definition and the exchange of Market Messages, a Tariff Interoperability User shall be treated as if it is a Market Participant. Tariff Interoperability Supplier Register TI Supplier Register means the register held by RECCo, detailing the Supplier Endpoints for each Tariff Interoperability Energy Supplier required or choosing to share Tariff Pricing Data under the Tariff Interoperability Arrangements. Tariff Interoperability User TI User means any individual or organisation which wishes to access the Tariff Pricing Data. “ c) after the term “Tariff Page” insert new definitions as follows: “ Tariff Pricing Data means: (a) (for electricity supply) Charges for the Supply of Electricity (as defined in the Electricity Supply Licence), but excluding any charges for the provision of Metering Equipment; (b) (for the supply of gas) Charges for the Supply of Gas (as defined in the Gas Supply Licence), but excluding any charges for the provision of Metering Equipment; and (c) (for the purchase of electricity generation or export) Export Tariffs (as defined in the Tariff Interoperability Licence Condition). “ 5. After Schedule 34 insert a new Schedule 35 as follows: “Schedule 35 Tariff Interoperability Arrangements SCHEDULE 35 Tariff Interoperability Arrangements Version: 1.0 Effective Date: 18 May 2026 Domestic Suppliers Mandatory for (i) Electricity Suppliers; and (ii) those Gas Suppliers that have opted to become (and still remain) a TI Energy Supplier. Non-Domestic Suppliers Mandatory for (i) Electricity Suppliers in the circumstances set out in the Electricity Supply Standard Licence Conditions; and (ii) Energy Suppliers that have opted to become (and still remain) a TI Energy Supplier. Gas Transporters N/A Distribution Network Operators N/A DCC N/A Metering Equipment Managers N/A Non-Party REC Service Users N/A Change History Version Number Implementation Date Reason for Change v0.1 N/A Initial draft for DESNZ review v0.2 N/A Draft for consultation v0.3 N/A Update to address consultation comments v1.0 18 May 2026 Modified by SoS 1. Introduction 1.1 This REC Schedule defines the Tariff Interoperability Arrangements, which involve Tariff Interoperability Energy Suppliers (TI Energy Suppliers) making available Tariff Pricing Data to Tariff Interoperability Users (TI Users). 1.2 The Tariff Interoperability Arrangements include requirements applicable to TI Energy Suppliers and the mechanism for accessing Tariff Pricing Data. Transition 1.3 Other than for the purposes of the development and testing of the Tariff Interoperability API in accordance with Paragraph 1.4, Paragraphs 2 and 3 (inclusive) of this REC Schedule shall only apply from 18 February 2027, or such later date as may be designated by the Secretary of State, being (in either case) the go-live date. 1.4 Before such go-live date: (a) for the purposes of this Paragraph 1 (and in the defined terms used in this Paragraph), references to TI Energy Suppliers which are required to provide Tariff Pricing Data under the Tariff Interoperability Arrangements shall be interpreted as if the Tariff Interoperability Licence Condition had already come into effect; (b) until this Code is amended to include the Tariff Interoperability API Technical Specification, the transition version of that specification maintained by RECCo, in consultation with the Secretary of State, shall apply; (c) each TI Energy Supplier shall develop a Tariff Interoperability API, compliant with the Tariff Interoperability API Technical Specification; (d) to the extent (if any) required by RECCo, each TI Energy Supplier shall participate in testing of their Tariff Interoperability API in cooperation with RECCo; and (e) each TI Energy Supplier shall provide its Supplier Endpoint to RECCo by 31 December 2026, or such later date as may be designated by the Secretary of State. Becoming and Ceasing to be a Tariff Interoperability Energy Supplier 1.5 Some Electricity Suppliers are required to participate in the Tariff Interoperability Arrangements by their Electricity Supply Licences. This REC Schedule together with the Tariff Interoperability Licence Condition sets out the obligations on Electricity Suppliers in relation to the Tariff Interoperability Arrangements, including the circumstances in which the sharing of information is mandatory. 1.6 Gas Suppliers are not mandated to share information under the Tariff Interoperability Arrangements but may choose to do so. In addition, Electricity Suppliers may also choose to participate in cases where they are not mandated to do so by the Tariff Interoperability Licence Condition. 1.7 Energy Suppliers which are not mandated to participate in the Tariff Interoperability Arrangements, but which wish to do so, shall notify RECCo of their intention to participate (thereby becoming a TI Energy Supplier). 1.8 Where a TI Energy Supplier has been participating in the Tariff Interoperability Arrangements on a voluntary basis and wishes to cease its participation, it shall give RECCo three (3) months' notice of the date upon which it will cease to participate. 1.9 Each TI Energy Supplier is required to comply with this REC Schedule while it is a TI Energy Supplier. An Energy Supplier which ceases to be a TI Energy Supplier under Paragraph 1.8 remains liable for any acts or omissions while it was a TI Energy Supplier. Tariff Interoperability Supplier Register 1.10 To support the Tariff Interoperability Arrangements, RECCo shall make available the TI Supplier Register providing TI Energy Supplier information in accordance with the Tariff Interoperability API Technical Specification. 1.11 The TI Supplier Register shall provide publicly available information relating to each TI Energy Supplier. This information shall include each Supplier Endpoint as well as TI Energy Supplier contact details to support query resolution. 1.12 Each TI Energy Supplier shall maintain its information held on the TI Supplier Register by raising a query via the REC service desk. RECCo shall ensure that the TI Supplier Register is updated within 2 Working Days of a change to the information being requested by a TI Energy Supplier. 1.13 RECCo shall retain an audit record of all changes to the TI Supplier Register for a minimum period of 15 months (with live data available for at least three months and archived data available for the remaining period). The system shall also be capable of accommodating the scrutiny of formal and informal audits by RECCo (or its agent), or any other person legally entitled to carry out such an audit. 1.14 RECCo shall issue a notification to TI Energy Suppliers in advance of Scheduled Maintenance that impacts the availability of the TI Supplier Register. Where an unplanned outage impacts the availability of the TI Supplier Register, RECCo shall issue a notification to each TI Energy Supplier as soon as is practicable. During any such outage, API requests will not be fulfilled, and requests will need to be re-sent by the TI Energy Supplier or TI User at a later time. 2. Tariff Interoperability Energy Supplier Requirements 2.1 Each TI Energy Supplier shall develop and maintain a Tariff Interoperability API, compliant with the Tariff Interoperability API Technical Specification. 2.2 Each TI Energy Supplier shall respond to requests for Tariff Pricing Data submitted in accordance with the Tariff Interoperability API Technical Specification, using Tariff Interoperability Market Messages consistent with the definition set out in the Data Specification. 2.3 Where this REC Schedule references notifications to TI Energy Suppliers this must be done via an email or REC Portal notification using the operational contact details provided by the TI Energy Supplier in accordance with Paragraph 2.5. TI Energy Suppliers shall ensure that their contact details are maintained for this purpose. Sharing Tariff Pricing Data 2.4 Each TI Energy Supplier shall provide RECCo with Supplier Endpoint details for the TI Energy Supplier's Tariff Interoperability API, specifying the relevant Market Participant Identifier(s). A single Supplier Endpoint could be utilised for multiple Market Participant Identifiers. Where a TI Energy Supplier proposes to amend its Supplier Endpoint details, it shall provide updated details to RECCo at least 2 Working Days prior to the change. TI Energy Suppliers shall take reasonable steps to limit the frequency of change to their Supplier Endpoint(s). 2.5 When providing Supplier Endpoint details, each TI Energy Supplier shall identify an operational contact for managing queries. 2.6 Subject to Paragraph 2.8, each TI Energy Supplier shall ensure that Tariff Pricing Data relating to all cases mandated by its Energy Supply Licence is available on request via the Tariff Interoperability API using the Supplier Endpoint details held within the TI Supplier Register. When providing Tariff Pricing Data, TI Energy Suppliers shall ensure that all relevant information impacting the overall cost to the Consumer is shared. The free text ‘Tariff Comments’ field should be used to specify additional information such as pass through costs or incentive arrangements which impact the overall cost to the Consumer. 2.7 Tariff Pricing Data may include ‘effective from’ and ‘effective to’ dates which enable the recipient to determine the period over which the Tariff Pricing Data is applicable. Where Tariff Pricing Data is changing, the TI Energy Supplier shall ensure that amended Tariff Pricing Data is available via the Tariff Interoperability API at least 60 minutes in advance of the change taking effect. 2.8 A TI Energy Supplier may suspend access to Tariff Pricing Data where: (a) a potential, confirmed or suspected event that could compromise the security or integrity of the Tariff Pricing Data and/or the Tariff Interoperability Energy Supplier's Systems is detected, and suspending access is a proportionate mitigation; (b) the number of requests for Tariff Pricing Data reaches the rate limit of 10,000 requests per second; (c) the number of requests for Tariff Pricing Data from a single IP address reaches the rate limit of 1,000 requests per second; or (d) requested to do so by RECCo. Non-Functional Requirements 2.9 Subject to Paragraph 2.8, each TI Energy Supplier shall ensure that: (a) Tariff Pricing Data is available via their Tariff Interoperability API 99.9% of the time, measured across each calendar month; (b) it retains a record of Tariff Pricing Data updates for a minimum 15 months (with live data available for at least three months and archived data available for the remaining period); and (c) it facilitates the retry strategy set out in Paragraph 2.16, where a response to a Tariff Pricing Data request is rejected, such that it buffers undelivered messages for a minimum of 12 hours from the initial attempt. 2.10 Each TI Energy Supplier shall ensure that it has sufficient capacity to support: (a) a steady state volume of at least 1,000 requests per second for Tariff Pricing Data; and (b) a peak volume of at least 5,000 requests per second for Tariff Pricing Data for any 5 minute window. 2.11 Each TI Energy Supplier shall provide a response to each request for Tariff Pricing Data within the following times: Performance Parameter Performance Level Up to and including steady state volume (as per Paragraph 2.10). 95th percentile response time of 1 second, measured across a calendar month. Above steady state volume and up to and including peak volume (as per Paragraph 2.10). 95th percentile response time of 5 seconds, measured across a calendar month. Error Resolution 2.12 TI Energy Suppliers shall validate each request for Tariff Pricing Data to ensure that: (a) the request aligns with the required format (as specified in the Data Specification); (b) the request relates to Tariff Pricing Data, which is in scope of the Tariff Interoperability Arrangements, either via Tariff Interoperability Licence Condition obligations or on a voluntary basis; and (c) the request relates to a Premises, which is in scope of the Tariff Interoperability Arrangements, either via Tariff Interoperability Licence Condition obligations or on a voluntary basis. 2.13 Where a request for Tariff Pricing Data fails validation, the TI Energy Supplier shall issue a rejection message using the relevant error code defined in the Tariff Interoperability API Technical Specification. 2.14 Each TI Energy Supplier shall provide a mechanism to enable queries regarding the Tariff Interoperability API to be raised by TI Users and potential users of the Tariff Interoperability API. 2.15 Each TI Energy Supplier shall ensure that they have policies and procedures in place to manage Consumer queries and complaints regarding the Tariff Interoperability Arrangements. 2.16 Where a Tariff Interoperability Market Message is sent by the TI Energy Supplier, resulting in validation by the recipient failing, or the response from the recipient is not received, the relevant Market Message shall be re-sent in accordance with the retry strategy. The retry strategy requires the TI Energy Supplier to retry delivery three times at 20 second intervals and then every 60 minutes until the buffer period in Paragraph 2.9(c) expires. Monitoring and Reporting 2.17 To support assurance of a TI Energy Supplier’s compliance with its requirements under the Tariff Interoperability Arrangements: (a) RECCo shall request Tariff Pricing Data via the Tariff Interoperability API to assess compliance with the Tariff Interoperability API Technical Specification and the non-functional requirements defined in this REC Schedule; and (b) each TI Energy Supplier shall submit a monthly report including the required information as defined in the Performance Assurance Report Catalogue. 2.18 For the avoidance of doubt, monitoring is limited to compliance with the Tariff Interoperability Arrangements and does not measure the accuracy of the data shared by TI Energy Suppliers. 2.19 Performance data referenced in Paragraph 2.17(b) shall be made available to RECCo to support performance assurance activities. Information may also be shared with the Secretary of State and / or Ofgem where requested. 3. Tariff Interoperability Processes 3.1 This Paragraph 3 defines the end-to-end processes for sharing Tariff Pricing Data under the Tariff Interoperability Arrangements. 3.2 To ensure that the Tariff Interoperability Arrangements are effective, a TI Energy Supplier can reasonably expect a TI User to: (a) ensure requests for Tariff Pricing Data comply with the format defined in the Tariff Interoperability API Technical Specification; (b) monitor error messages received in relation to requests for Tariff Pricing Data; (c) where a request is rejected, make reasonable attempts to re-send the request in accordance with the retry strategy defined in Paragraph 2.16 and check the TI Supplier Register before raising a query with the TI Energy Supplier; and (d) where a request remains undelivered after a reasonable number of attempts have been made, to raise a query with the relevant TI Energy Supplier using the lead contact details provided within the TI Supplier Register. Access to Tariff Pricing Data 3.3 A TI User wishing to access Tariff Pricing Data shall follow the process in the interface table below: Ref When Action From To Interface Means 3.3.1 As required. Request details of Supplier Endpoints. The TI User shall determine how frequently they request Supplier Endpoint details. These are not expected to change on a regular basis. TI User TI Supplier Register Get Supplier Tariff Endpoints Request TI API 3.3.2 Following 3.3.1 wher e the message passes validation. Provide details of all available Supplier Endpoints. TI Supplier Register TI User Get Supplier Tariff Endpoints Response TI API 3.3.3 Where Tariff Pricing Data is required. Submit request for a list of available Tariff Ids. TI Users can apply query parameters to filter the response as set TI User TI Energy Supplier Get Tariffs Request TI API out in the Tariff Interoperability API Technical Specification. 3.3.4 Following 3.3.3 where the message passes validation. Share requested Tariff Ids. TI Energy Supplier TI User Get Tariffs Response TI API 3.3.5 At any time, where the TI User knows the Tariff Identifier. Submit request for Tariff Pricing Data using the Tariff Id. TI User TI Energy Supplier Get Tariff Details Request TI API 3.3.6 Following 3.3.5 wher e the message passes validation Share requested Tariff Pricing Data. TI Energy Supplier TI User Get Tariff Details Response TI API “ Funmi Brady 13-05-2026 Signed as an official of the Department for Energy Security & Net Zero authorised to act on behalf of the Secretary of State.