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tsc-rs: an agent-built TypeScript compiler, and what the model choice cost
Theo released tsc-rs (also called ts-rust), a full Rust rewrite of the TypeScript compiler, type checker and LSP. He describes it as an open-source drop-in replacement for tsc (repo) . Agents had been working on it for five months. In his words: "I burned ~$400k of Codex tokens and got nowhere. Burned ~$20k of Opus and got there in 2 weeks." He also says he has not read a single line of the code . He adds that the Opus usage equals about 10 weeks on the $200 Claude subscription .
The port matched its test oracle, upstream TypeScript, closely. Of the first five issues filed, he says four were real upstream TypeScript behaviour that the port reproduced faithfully . He is open about its limits. bun check shipped the same day and is "probably the right choice for most apps using Bun," and tsc-rs is only faster when you use Effect TS checks. He prefers tsc-rs for its drop-in compatibility, WASM readiness and built-in Effect mods .
Mario Zechner and Armin Ronacher explained in a separate conversation why projects like this work. If you have "an Oracle that can tell the LLM if what it did is correct or not, then you basically won." Bun's test suite is enough for agents to drive a port with occasional steering . Ronacher had agents implement every format in a serialization library from sample TOML, CBOR, MessagePack and JSON files, then told them to "fuzz the hell out of it." That found many bugs, and an LLM can reason about cases a fuzz generator misses .
Haiku 5.5: Anthropic's pitch is a cheap subagent
Anthropic says Haiku 5.5 is in Claude Code and the Claude Platform, costs about 75% less to run than Haiku 4.5, and suits use as a subagent under Opus 5.5 or Sonnet 5.5. It suggests "summaries, compactions, or database queries" . Addy Osmani says his team "loves it as a subagent alongside Opus 5.5," and notes it has an adjustable effort setting . Cursor has it under Settings > Models. Pricing is $0.10/$0.50 per million input/output tokens, rising to $0.50/$2.50 above 100k input tokens. Sonnet 5.5 cache reads dropped from $0.20/M to $0.10/M .
Simon Willison found catches that change the routing math:
- Up to 100k tokens it costs exactly the same as GPT-6 Luna. Above that, its price rises 5x, while Luna's goes up only at 272k and only to $0.20/$0.75. For long-context jobs, Luna looks like the better deal .
- The new tokenizer used about 1.25x as many tokens as Haiku 4.5 on the same long prompt, which amounts to a hidden price increase .
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You can't turn reasoning off. The default is
medium. To try it:llm install -U llm-anthropic,llm anthropic refresh, thenllm -m claude-haiku-5.5 ... -o thinking_effort low. - Max and Team subscribers now get monthly API credits: $100 for Max 5x, $200 for Max 20x, and up to $500 pooled for Team. They don't roll over. You can turn off auto-reload so requests stop when the balance runs out .
ThePrimeagen offers an early counterpoint. Dropping Haiku in for Luna, both with reasoning off, took a one-line config change. Haiku "performed significantly worse" and was slower on both passes and failures, and he doesn't yet know why . Separately, he found OpenAI's new decision model much faster and more accurate than his previous setup at finding click targets in Omarchy QA screenshots . Benchmark your own automation before switching.
Cross-model adversarial review takes one sentence
DHH's technique: when you're driving from Codex, say "Review this with claude", and when you're in Claude, say "Review this with codex". The models know how to start a review through the CLI, take turns and settle an argument. "No magic" . He describes the rest of his setup as "any harness, multiple agents concurrently, barely any skills, and using adversarial reviews" . Theo runs a version of this. Claude spins up Sol subagents and calls Codex through T3 Code to review its work, because he finds OpenAI models "a bit more thorough with their analysis." He still calls the Claude plan "absolutely mandatory" for shipping serious engineering work . On the "nerfed" $200 Codex plan, he argues that cost per task matters more than tokens per dollar. In his own Terminal Bench run, 6.1 Sol at x-high roughly tied Opus 5.5 at about one-thirteenth the cost per task .
Audit your agents for logic they keep reinventing
Theo says his agents wrote over 200 bad "watch PR" scripts. His audit prompt: "audit my history with Claude Code, Codex and other agents on this machine. Look for every time I asked for a PR to be watched or babysat." Then ask how many times the logic was reinvented, how many versions had visible flaws, and roughly how many tokens and dollars were wasted . The production fix in T3 Code took about 30 tries. It replaced CLI calls with direct API calls and switches between GraphQL and REST depending on which uses rate limits more efficiently, with fallbacks. That cut rate-limit usage by over 75% .
Huntley: Nix as the shared environment for agent sandboxes
Geoffrey Huntley argues for a single devenv.nix as the one source of truth for laptops, CI and ephemeral agent sandboxes. His example stanza provides Rust, Postgres, a rustfmt hook and prek "for agent backpressure" . He develops on NixOS and explicitly tells agents to use sudo, counting on rollback. With runNixOSTest, he puts the whole OS, including multi-machine networking and firewall rules, under test . He also uses an overlay to strip force-push out of the Git binary inside agent sandboxes (nix-demo) . The tradeoff he names is that incremental caching is weaker than in Bazel or Buck2 . Separately, he says he is dropping Opus 5.5 because Claude Code's classifier "is too paternalistic and breaks my flow/development loops" .
Smaller items
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Deep Agents skills: you can now bind tools to a skill with
metadata.include_tools. A bound tool stays out of context until the agent reads that skill . Apps can passpinned_skillsso a skill like/meeting-prepis loaded before the first model call . Settingskills_metadata=Nonemakes the next run rescan the skill library . - Sourcegraph Deep Search lets Claude Code search code you haven't checked out. Their demo finds deprecated packages across Kubernetes .