# OP Stack Compatibility OP Stack's standard execution client (`op-geth`) strictly order transactions by priority fee (gas price). However, SBB requires preconfirmation of inclusion order before the transaction contents are decrypted, meaning transactions must follow a first-come, first-served (FCFS) order based on the encrypted arrival time. This deterministic ordering logic is fundamentally incompatible with the OP Stack’s default `tx_list` block production mechanism. **To maintain compliance and alignment with the Superchain, and avoid modifying core OP Stack logic, we integrate SBB using a specialized sidecar architecture (**Rollup Boost + a modified `rBuilder`). *** #### SBB Integration: Rollup-Boost + rBuilder Sidecar Our integration solution leverages Flashbots' Rollup-Boost technology alongside a custom rBuilder implementation. * **Rollup-Boost**: This functions as a bridge between OP Stack's `op-node` and `op-geth`, preserving canonical interfaces. * **rBuilder**: This is the external, modular block builder that incorporates SBB's logic. It is modified to incorporate SBB's cryptographic ordering constraints (FCFS pre-confirmation logic) when constructing the transaction payload. This sidecar integration ensures we can fully support SBB while maintaining full alignment with Superchain governance and upgrade paths. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.theradius.xyz/overview/secure-block-building-sbb/op-stack-compatibility.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.