BLS deck: why we built the emulator, funding, versions and releases, Axiom, What's next

[MaxGhenis]

Max's two items from yesterday's prep meetings (the motivation slide and the forward-looking close), plus Thesia Garner's question list (email of October 7) worked into the deck. Max asked for the answers to go where each one fits rather than on a slide of their own.

What changes

• New slide 7, "Why we built a TAXSIM emulator" (1 min, Max). The hero is BEA running PolicyEngine for 2021 onward. The cards: microsimulation first (launched 2021); state taxes and TAXSIM35 validation both starting in April 2022 (#715, #704), with all states by April 2024; NBER's successor line from taxsim.nber.org; and one model serving both uses. The notes carry the spoken setup and what not to say: BEA's "discontinued" footnote, the "fully compatible" line, and anything about Dan Feenberg's plans.
• PolicyEngine today (slide 5) gains a funding strip (the PSL Foundation as fiscal sponsor, plus the funders on the public supporters page). Recounted today: 4,932 YAML test files (the slide said 4,693) and 136 contributors (it said 133). The notes answer the funding and staffing questions.
• New slide 13, "Versions and releases" (2 min), in the emulator section before the demo:
  • 286 PolicyEngine US releases and 15 emulator releases in the last 90 days.
  • Every release computes every tax year.
  • The pin command uv tool install policyengine-taxsim==3.0.1 --with policyengine-us==2.25.2 resolves (checked with uv pip compile).
  • Changelog typing, support on the public tracker (median first reply to NBER's reports: 23.5 h), and the 3.0.0 S-corporation default change.
  • The notes answer the release-schedule, version-notes, tax-law-change-list, input/output-change and support questions, with the honest caveats: the output has no version stamp, PyPI holds PolicyEngine US only from May 2026 onward, and the documentation's pin example (1.555.0) is no longer on PyPI.
• Section 05 is now "What's next": the 2026 rules (moved up), then new slide 29, "Axiom: our next-generation rules engine" (2 min), then the CE pilot. The Axiom slide has three stages:
  • Today: PolicyEngine US powers the emulator.
  • Planned: Axiom on the backend, with PolicyEngine wrappers.
  • Throughout: backwards compatible, and we keep powering TAXSIM as long as it is needed.
  • Its footnote states the boundary: Axiom does not yet compute a complete federal return (rulespec-us #1318).
• Notes on existing slides now carry the matching answers: in-kind valuation (NSLP, WIC, Medicaid) on slide 25, testing on slide 16, the annual update on slide 28, and the open-source logic on slide 4. The agenda notes map every question to its slide.
• Timing stays at 60 minutes plus 30 of Q&A. Added: why-emulator 1, releases 2, axiom-plan 2, and a 2-minute Axiom walk-through still to come in a follow-up commit. Trimmed: what-is-pe 3→2, nber 3→2, demo 13→10, imputation 3→2, ce-pilot 3→2.

Every figure was checked this morning against PyPI, the GitHub API, the policyengine-us and rulespec-us trees, taxsim.nber.org, the BEA technical document and policyengine.org. An adversarial pass removed one claim: the Axiom-vs-TAXSIM federal run on 87,519 tax units, which compares Axiom with a 2026 TAXSIM test build rather than with the emulator.

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Project	Deployment	Actions	Updated
policyengine-slides	Ready	Preview	Oct 8, 2026 5:45pm UTC

[MaxGhenis]

Merged at reviewed head ef76850 after:

• two-lens review (claims + build) at 577a845: approve with fixes, all applied;
• delta review of the restructure at 8494e1a: approve, nits applied;
• final independent review (Subfleet, standard tier) of 5793df8..ef76850: approve, conditional on tsc and eslint, both of which pass locally.

CI green (Build, Lint, Tests, Vercel). Deck as presented at BLS on 2026-10-08.

🤖 Generated with Claude Code