Sasha Rush prototypes Lean-verified Rust tokenizer for agentic RL training
Overview
Sasha Rush has prototyped a Rust tokenizer and agent pipeline whose key properties are formally verified in Lean, according to RadixArk, which praised the work on X. The prototype addresses training-inference mismatch in reinforcement learning by verifying the tokenizer pipeline itself, rather than relying on chat messages built with Jinja templates.
RadixArk says the approach extends Miles' token-in-token-out idea, which tests that training sees the exact tokens the model generated, into formal verification. The source reports no benchmarks or release date for the prototype.
Written by AI from the articles below · updated Oct 27, 8:06 PM ET
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RadixArk@radixarkOfficialRadixArk praises Sasha's Lean-verified Rust tokenizer for agentic RLAIRadixArk praises Sasha's work formally verifying properties of a Rust tokenizer in Lean, which extends Miles' token-in-token-out idea beyond testing that training sees the exact tokens the model generated. Sasha's prototype, posted by Sasha Rush (@srush_nlp), addresses training-inference mismatch in RL by verifying the tokenizer pipeline rather than relying on messages built in Jinja.
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