--- title: "Foxl v0.2.16: Claude Code OAuth, Reborn as a Compatibility Layer" description: "How Foxl translated request formats and model identifiers for a Claude subscription path, including routing limits and tradeoffs." author: "Foxl Team" date_published: "2026-04-21" date_modified: "2026-07-16" canonical_url: "https://foxl.ai/blog/v0-2-16" markdown_url: "https://foxl.ai/blog/v0-2-16/index.md" image: "https://foxl.ai/blog/claude-code-compat.png" social_image: "https://foxl.ai/blog/social/v0-2-16.png" content_type: "Deep dive" topics: ["Protocol translation","OAuth","Model routing"] products: ["Foxl Agent","Foxl Relay"] --- # Foxl v0.2.16: Claude Code OAuth, Reborn as a Compatibility Layer > Live probes showed that system-prompt and tool-name shapes changed observed Claude subscription routing. Foxl shipped a compatibility layer, then documented the limits of treating provider behavior as a stable contract. - Author: Foxl Team - Published: 2026-04-21 - Last reviewed: 2026-07-16 - Reading time: 3 minutes - Canonical HTML: [https://foxl.ai/blog/v0-2-16]() ![A compatibility layer translating Foxl agent requests into the protocol and model identifiers accepted by the Claude subscription path.]() Published on April 21, 2026, this post records the [Claude Code OAuth compatibility mode]() shipped in Foxl v0.2.16. It describes the request shape and model catalog at that release, not a permanent contract with Anthropic. ## Shipped behavior v0.2.16 re-enabled the Claude Code OAuth provider after v0.2.15 had hidden it. The selectable models at release were Opus 4.7 and Sonnet 4.6. Requests still used the user's Claude Code credentials, but Foxl changed the payload at the transport boundary before sending it to Anthropic. The change was based on live probes that observed different subscription routing when Foxl sent its normal system prompt and native tool names. Those observations justified a compatibility path for this release, but they did not establish a documented or stable Anthropic API guarantee. ### System prompt rewrite The transport left the Claude Code preamble in the `system` field. Foxl's persona and workspace context moved into a `` prefix on the first user message. The agent still received that context, but with lower instruction precedence than a system message. ### Tool adapter Four Foxl tools were exposed under Claude Code compatible names: - `exec` as `Bash` - `file_read` as `Read` - `code_search` as `Grep` - `web_fetch` as `WebFetch` Each wrapper translated the model's Claude Code shaped input back to the existing Foxl callback. For example, the `Bash` wrapper converted a millisecond timeout to the seconds expected by `exec`. If several Foxl tools mapped to one wire name, the adapter kept one owner and dropped the rest. ## Implementation implication Compatibility mode changed the tools visible to the model, not just their labels. Memory, workspace memory, subagents, schedules, channel sends, browser controls, image viewing, and other tools without an adapter were omitted. A conversation using this provider therefore had a smaller capability set than the Anthropic API key and Foxl relay paths. The rewrite lived in `compat/message-rewriter.ts` and `compat/tool-adapter.ts`, with the transport invoking both before the HTTP request. The [Strands tool callbacks]() remained the execution layer after a supported tool call was translated. ## Known limitation and follow-up OAuth endpoint behavior, subscription eligibility, model access, and usage accounting are controlled by Anthropic. Foxl could shape requests and report failures, but it could not guarantee that a request would always use a particular allowance. Users needing the full Foxl tool registry had to use [another configured provider](). ### Correction: April 22, 2026 v0.2.17 briefly bypassed the tool adapter and re-added Haiku 4.5 after raw API probes accepted native Foxl tools. v0.2.18 reverted that change the same day because full Strands agent requests still produced "out of extra usage" failures. The raw probe did not reproduce the production request shape. The compatibility adapter returned to the supported path. ### Correction: July 16, 2026 The model list is no longer limited to the two v0.2.16 entries. Current source lists [Fable 5](), Opus 4.8, Opus 4.7, Sonnet 5, and Sonnet 4.6 for Claude Code OAuth. The legacy `claude-code/opus` alias now resolves to Opus 4.8. Haiku aliases remain for persisted selections, but Haiku is not in the selectable OAuth catalog. The request and tool compatibility layer is still active. ## How to verify - Select Claude Code OAuth and confirm the provider reports available credentials. - Ask the agent to read a file, search code, or run a harmless shell command. Those calls should execute through `Read`, `Grep`, or `Bash`. - Check the server log for `[CompatTools]`. It reports the tool names kept and dropped for that invocation. - Use the credential-gated scripts under `foxl/scripts/test-claude-code-oauth-*.mjs` for a live transport check. They contact Anthropic and may consume account usage. ## References and further reading 1. [Configure model providers]() - Documentation 2. [Current model compatibility]() - Documentation