Fx v0.0.16

fx uses 41% fewer tokens. The CLI is 2.8% smaller. libfx npm downloads are about 60% smaller. Edit files up to 4× larger, now up to 16 MiB.

Improvements

• Long agent turns use less CPU. A paired local benchmark with 1,000 tool steps used 50–59% less CPU than the previous implementation.
• fx update now works as an alias for fx upgrade, including --channel and --json.
• Tool results keep their original timestamps when a turn is rebuilt or resumed.
• The macOS arm64 CLI binary is 2.8% smaller (5.97 MiB vs 6.15 MiB), saving 180,576 bytes.
• Installing libfx downloads about 60% less than 0.0.15, including the matching native platform package. On Apple Silicon, the download drops from 19.08 MB to 7.32 MB, a 61.6% reduction.
• Across macOS and Linux builds, total libfx npm downloads are 60.1–61.6% smaller. Unpacked package contents shrink from 43.55 MB to roughly 18–19.4 MB.
• libfx installs the native addon for your platform instead of carrying every platform’s binary. By default, Node.js loads the WebAssembly backend only when native execution is unavailable.
• Across ten model families, caching scenarios used 41% fewer uncached input tokens than 0.0.15. Requests that broke the cached prompt prefix fell from 80 to 10, an 87.5% reduction.
• Uncached input tokens fell 79% on Claude Sonnet 5.5, 78% on Claude Haiku 5.5, and 76% on GPT-6.1 in that comparison. Results varied by model, with MiniMax using 3% more.
• Prompt caching on supported models now reuses shared instructions across workspaces and worktrees.
• Changing branches or permissions, reading new folder rules, and resuming a conversation keep the earlier conversation available for prompt caching.
• Named skills send their full instructions with the turn that invokes them instead of adding them to every later request.
• Browser apps can bundle only the WebAssembly module they use instead of both the agent and terminal modules.
• The libfx WebAssembly core is 12.8% smaller than in 0.0.15 (2.16 MiB vs 2.47 MiB), and the terminal is 20.1% smaller (3.39 MiB vs 4.24 MiB). These are uncompressed binary sizes.
• edit_file and write_file handle files up to 16 MiB, up from 4 MiB.
• File edits save their diffs instead of full copies of the file before and after every change. The diff remains available in Ctrl+O after resume, with an omitted-row notice if it exceeds the saved-text limit.
• /model finds models from abbreviated or slightly mistyped provider and model names.
• Saved sessions retain token usage from each model reply, including replies received before an interrupted turn, and continue counting after resume.
• Subagent token usage is saved in each subagent’s own session and remains separate from its parent’s total.
• fx ask --json includes cached-read and cache-write token counts when the provider reports them.
• Global ~/.fx/AGENTS.md can link to an instruction file elsewhere inside your home directory.
• Slack sign-in requests the permissions needed to search private channels and direct messages you can access.

Bug Fixes

• When repeated response failures stop a turn, fx keeps its prompt, partial reply, and completed tool calls. The next prompt can continue from that work, including after resuming the session.
• Retrying a cancelled libfx prompt with the same turn ID returns the ended turn instead of running the prompt and its tools again.
• Opening an edit in Ctrl+O no longer crashes when the file contains terminal escape sequences.
• Editing files containing invalid UTF-8 no longer prevents the session from saving or stops the turn. Invalid bytes appear as readable escapes in previews and saved diffs.
• Fixed fx balance startup when reading a saved credential from the system key store.
• Stopping a terminal also stops commands running in nested shells and separate job-control groups instead of leaving them running.
• MCP server failures retain their final error output, including when the server exits immediately.
• /usage in the browser terminal fetches usage through the host instead of showing zero because WebAssembly cannot make native network requests.
• Qwen no longer fails after its first tool call with System message must be at the beginning.

Security

• File diffs display terminal control sequences as text instead of letting them alter the terminal. This also applies when opening older saved conversations.
• Commands with escaped or separated stderr-redirection descriptors require review instead of being mistaken for routine commands that can skip review.
• fx login codex rejects account identifiers that cannot be used in HTTP headers before saving credentials or reporting success.
• File, tool, and skill text is escaped so it remains separate from fx’s own context and permission updates.

Breaking Changes

• libfx now requires Node.js ^20.19.0 || >=22.12.0, including when loaded with require().
• libfx 0.0.15 cannot reopen saved turns containing the new context updates. Upgrade every worker sharing their session store before starting new turns.