libfx is now durable out of the box. Same API on local, Vercel and DIY. Use your ChatGPT or Grok subscription, or a custom provider, to power cloud agents with libfx. fx moves to Zig 0.17.

New Features

• Durable libfx sessions can continue after crashes, redeploys, and function timeouts. Interrupted tools run again only when marked idempotent: true.
• You can run multiple named libfx agents in one app, each with its own model, instructions, and tools. Sessions stay with the agent that created them.
• wakeHandler() provides an HTTP handler for queued prompts and recovery, so one Vercel route serves all your libfx agents.
• Each libfx session can override its agent's model, reasoning effort, and instructions.
• libfx now supports ChatGPT and Grok subscriptions for server-side agents, with sign-in helpers included.
• libfx agents can connect to custom OpenAI-compatible endpoints, including local model servers.
• Clients can reconnect to a libfx reply stream from the last event they received, even through a different server.
• Another server process can steer or cancel a running libfx session, or resume an interrupted turn.
• Prompts sent to a busy libfx session queue behind its running turn and start when it finishes.
• Reusing a libfx messageId follows the original turn instead of starting it again.
• libfx now includes TypeScript types for its public APIs.
• Pass hooks to createFxAgent() or createFxEngine() to observe model calls, tools, approvals, subagents, and saved-session activity on native and WebAssembly backends. Content capture is opt-in, and callback failures do not interrupt or retry agent work.
• With --sessions-v2, opening a session saved in the previous format converts it together with its subagent sessions. The previous-format files are removed only after the converted sessions are saved.
• Use fx --sessions-v2 sessions convert to convert all sessions saved in the previous format at once.
• On Vercel, libfx can use deployment OIDC credentials instead of an API key.
• createFxEngine() adds queued follow-ups with followUp() and lets you withdraw pending steering with turn.withdraw().
• /usage and fx usage now show your provider's usage reports instead of locally recorded usage.
• AI Gateway usage shows your spending and budget, or the selected API key's spending, with per-model totals.
• /usage now shows ChatGPT plan limits and activity, plus Grok allowances, credits, and pay-as-you-go spending.
• In @ file suggestions, Enter mentions the selected folder; Tab opens it.
• ACP clients can toggle Fast mode on supported models and keep the setting when resuming.
• fx models --json now lists Gateway model names, reasoning levels, and Fast and Ultrafast support.
• fx status --json now reports the starting permission mode, available modes, and reasoning effort.
• Compatible terminals can show when fx is working, finished, or waiting for your input.
• Commands launched by fx receive AI_AGENT=fx, so development tools can detect the agent environment.

Improvements

• Prompts now appear immediately after Enter, even in long conversations.
• On Vercel, libfx starts idle sessions in the request that submits the prompt instead of waiting for a queue delivery.
• libfx waits to read a reply stream until its events or result are requested.
• Native libfx reuses HTTP connections between turns without delaying streamed output.
• libfx shares token refreshes across sessions and supports refreshLock for multi-server apps.
• @ suggestions reuse a saved workspace index, and file-content searches run in parallel.
• @ suggestions rank exact file names, name prefixes, and whole-word matches above scattered letters. Searches can span a file's containing folder and its name, and highlighted letters show the match used to rank it.
• Short @ searches and searches with many exact matches return faster. The file picker shows up to 10 rows when the terminal has room.
• Repeated file searches use less memory during long turns.
• grep_files now searches files larger than 200 KiB and reports when results are incomplete.
• ctrl+o now wraps long commands and tool details instead of cutting them off.
• /usage opens with cached numbers and refreshes in the background. Press r to refresh manually.
• Shell tracing now includes startup-step timings for diagnosing slow launches.
• Embedded browser terminals can load your workspace's AGENTS.md through the host adapter.
• ACP sessions start in your saved permission mode and remember changes for future CLI and ACP sessions.
• Image-heavy requests keep the newest images and omit older ones when needed, without changing saved history.
• Request-size errors trigger a retry with fewer images before compaction.

Bug Fixes

• Long submitted prompts and steering messages no longer overwrite earlier scrollback.
• ctrl+o keeps your reading position when running commands change the transcript above it.
• File searches pick up newly created files and respect parent and global ignore rules.
• grep_files no longer hangs when it encounters a named pipe.
• An empty or relative HOME no longer crashes fx or puts profile files in the current folder.
• Shell commands no longer fail when a child process exits in gVisor sandboxes, including Modal.
• Switching models or providers in ACP turns off Fast or Ultrafast when the new model does not support it.
• Embedded terminals apply Fast and Ultrafast to their first request without opening the model picker.
• libfx tool failures include an error message even when the tool throws an empty error.
• libfx saves each tool result as it finishes, so recovery can reuse completed work.
• Interrupted libfx tools no longer appear to run forever after recovery. Their events report that the call may have partly run.
• libfx rejects checkpoints created by a newer version instead of attempting to restore them.
• A steer that starts a durable libfx turn is no longer applied twice or dropped when it contains images.
• Cancelling a durable libfx session no longer stops a queued prompt that starts after the cancellation. Steering already assigned to another queued prompt no longer reaches the running turn.
• Usage totals stay visible when a refresh fails or the local cache becomes unreadable.
• Gateway requests no longer fail intermittently at startup.
• libfx rejects invalid host HTTP statuses instead of crashing the process.
• Markdown rendering no longer crashes on incomplete UTF-8.

Security

• Workspace indexing and fx's built-in read-only Git checks no longer run repository-configured programs.
• Auto mode no longer reruns a refused built-in Git check without its protections.
• Local usage data is saved with owner-only permissions.
• Vercel and local libfx storage reject writes from a worker that has lost ownership of the session.
• libfx keeps credentials out of saved conversations and adds them only to the selected service's HTTP calls.
• libfx masks keys and tokens echoed in failed provider responses.
• Grok token refresh rejects credentials belonging to a different account.
• libfx sign-in helpers reject pasted callbacks from a different sign-in.
• Custom libfx endpoints require HTTPS outside localhost.
• libfx routes queued work to the named agent on the intended store, rather than another store with the same agent name. Use a separate world() store for each customer whose sessions must stay separate.
• libfx ignores queue deliveries that do not refer to an input already saved by the app. A delivery cannot replace that input or its caller context and session settings; apps must still authorize session access and authenticate their queue routes.

Breaking Changes

• macOS release binaries now require macOS 15 or later.

• Building fx from source now requires Zig 0.17.

• createFxAgent() now manages durable sessions. Use createFxEngine() for the previous single-conversation API.

• Tools passed to createFxAgent() must set idempotent: true or false to say whether a call can run again after a crash.

• Native libfx runs idempotent tools in parallel unless marked writes: true. Other tools run alone by default.

• Images sent to durable libfx sessions must be Base64-encoded. createFxEngine() still accepts image files and raw bytes directly.

• Disconnecting from a durable libfx turn no longer stops it. Use session.cancel() or an abort signal.

• In one process, libfx agents with the same name on the same store must use the same configuration. Creating a conflicting agent throws FX_AGENT_NAME_IN_USE; give different configurations separate names or stores.

• Durable libfx prompts and steers, including their context and session settings, must fit within 8 MiB of JSON. Larger inputs throw FX_INPUT_TOO_LARGE before anything is saved.

• ACP's code mode has been replaced by auto. Clients should use auto, ask, or full-access.

• /cost has been removed. Use /usage.

• fx usage --period now accepts today, 7d, and month. The 24h and 30d periods have been removed.

• fx usage --json now returns provider reports instead of the previous local usage totals.

• ACP usage updates report context use and no longer include costs.