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Framer Rebuilds Agent Harness to Execute Code During Streaming, Cutting Costs by Up to 33%

·2026.11.02 09:00

Key point

The new system compiles JavaScript into executable cells as the model generates them, reducing tool steps by 43% and cached input tokens by 39%.

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Details

  • Framer rebuilt its agent harness to execute JavaScript code while the model is still generating it, making workflows up to 33% cheaper and 20% faster.
  • The architecture uses 2x fewer tool steps and 39% fewer cached input tokens per message on average, with no measured reduction in quality.
  • Eager execution parses incoming code into executable cells using AST parsing, allowing document edits to begin before the full program is generated.
  • Early cancellation stops the remaining code stream if an assumption fails, saving output token charges and preserving already-applied edits.
  • The document access API was redesigned from a DSL to method calls, enabling efficient reads and writes via an in-memory copy in a Web Worker.
  • External agents like ChatGPT Desktop and Claude Code now use the same unified harness as the in-app agent, submitting single programs via MCP.
  • The team acknowledges prior work by Zhensu Sun et al. on "Executing as You Generate" in Python, noting they plan to adopt its buffer optimization.
javascriptmcpagent-harnessframerweb-workerstreaming-executionast-parsing
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