Dan Siroker
Co-Founder & CEO, Limitless; Partner, Rebel Fund at limitless
Reviewed Updated May 1, 2026This profile is AI-generated. If you spot an error, please help us fix it by sharing a URL to the correct information.
Background
Dan Siroker is the co-founder and CEO of Limitless (formerly Rewind AI), a personal AI memory product. He previously co-founded Optimizely, the experimentation and A/B testing platform.
Siroker was a Google product manager who left the company to join Barack Obama’s 2008 presidential campaign as Director of Analytics, where he applied A/B testing to email, donation pages, and volunteer sign-up flows on the campaign website 12. After the campaign, in 2010 he co-founded Optimizely with Pete Koomen, who had also been at Google 3. Optimizely was part of Y Combinator’s Winter 2010 batch and pivoted during the second week of the program 3. Optimizely raised more than $200 million from investors including Andreessen Horowitz, Index Ventures, GV, and Goldman Sachs, scaled to over 1,000 customers including Gap, StubHub, IBM, and The Wall Street Journal, and was acquired by Episerver in 2020; the combined company rebranded as Optimizely in January 2021 4. Siroker had stepped back from the CEO role at Optimizely in 2017 (Jay Larson took over) 4.
In 2020, Siroker founded Rewind AI with co-founder Brett Bejcek 5. Rewind began as a Mac application that recorded and indexed everything a user saw, said, or heard on their computer, making it searchable later. The company raised a seed round of approximately $10M from Andreessen Horowitz (led by David Ulevitch), First Round Capital, and others in November 2022 5. In summer 2023, Rewind raised a $12M Series A at a $350M valuation from New Enterprise Associates, conducted through an unconventional public fundraising process in which Siroker shared the pitch deck and routed investors to rewind.ai/invest; the campaign generated more than 170 preliminary offers 67. The company rebranded to Limitless and launched a wearable Pendant device in April 2024, expanding from desktop software to AI hardware 8.
On December 5, 2025, Meta acquired Limitless to bolster its push into AI wearables. Financial terms were not disclosed 9. Siroker also serves as an investing partner at Rebel Fund, a venture fund formed by Y Combinator alumni that invests in YC seed-stage startups 10.
Stated Thesis
Siroker has not published a formal angel investing thesis. In public commentary on AI and product building, he has emphasized application-layer value over model wrappers, the importance of transparency with investors, and ruthless prioritization. On thin AI wrappers, he said he believes that pattern “is likely going to go away” and that “the true value is in the app side” 7. On founder qualities, he has cited Paul Graham’s framing that “the best founders are relentlessly resourceful” 7.
Siroker’s public fundraising experiment for Rewind’s Series A also doubles as a public-facing thesis on how investors and founders should relate. He has said that “transparency breeds trust and trust is the most important thing we have,” and described the lead investor relationship as “a relationship I’m gonna have for decades” 7.
Inferred Thesis
The publicly verifiable angel portfolio for Dan Siroker is small. Tracxn lists six angel investments with four disclosed deal entries, all from a single 2021 cohort 11. Sample size is too small for reliable percentage breakdowns.
Qualitative pattern (4 verified rounds with dates):
- Stage: 100% seed (4 of 4) — Milk Video, Haystack, June, MindPortal 11
- Sector: Productivity software, video tooling, analytics, and brain-computer interface — clustering around tools that help individuals or teams capture, retrieve, or act on data. This is thematically adjacent to his operating focus at Optimizely (experimentation) and Limitless (personal memory).
- Geography: Primarily US (San Francisco / New York / Boston for Haystack), with at least one Singapore-based company in the broader Tracxn portfolio 11.
- Timing: All four dated investments fall within a three-month window in summer 2021 (May 25 – August 18), suggesting concentrated activity rather than steady deployment.
- Exits: Two of his disclosed angel positions have exited — ClearBrain (acquired 2020) and Milk Video (acquired June 2025) 11.
Rebel Fund participation: Through Rebel Fund, Siroker is associated with seed-stage Y Combinator companies more broadly. Rebel Fund has invested in more than 200 YC startups 10. Individual deal-level attribution to Siroker via Rebel Fund is not publicly broken out.
Notable gaps: Despite Siroker’s deep operating experience in marketing software, A/B testing, and (more recently) AI hardware and personal AI, the verified angel portfolio is too thin to determine whether his angel investing tracks his operating expertise. Founders considering him as an angel should treat his time and product judgment as the primary signal, not portfolio breadth.
Portfolio
This table includes only investments with independent source confirmation. Tracxn reports six total angel investments 11; four have disclosed deal data.
| Company | Year | Stage | Source |
|---|---|---|---|
| Milk Video | 2021 | Seed ($1.5M) | 11 |
| Haystack | 2021 | Seed ($1.2M) | 11 |
| June | 2021 | Seed ($2.36M) | 11 |
| MindPortal | 2021 | Seed ($5M) | 11 |
| ClearBrain | Pre-2020 | Angel (acquired 2020) | 11 |
| Navattic | 2022 | Seed ($4.25M, lead Canvas) | 1214 |
Two additional Tracxn portfolio entries are reported but not disclosed by name in publicly accessible records.
In Their Own Words
On AI wrappers and where value accrues:
“I do think that’s likely going to go away.” 7
“The true value is in the app side.” 7
On AGI hype cycles:
“AGI will be amazing…and then just like every other new technological innovation, three weeks later, people will assume it’s, take it for granted.” 7
On fundraising in public:
“Transparency breeds trust and trust is the most important thing we have.” 7
“I view this, the person who’s gonna lead this round…as a relationship I’m gonna have for decades.” 7
On focus and prioritization in product building:
“The main thing is that the main thing should stay the main thing.” 7
“I view everything we do…by the amount of impact it will have divided by the effort.” 7
“I’d rather hold time and quality as the kind of the goals and then cut scope ruthlessly.” 7
On founders:
“The best founders are relentlessly resourceful.” 7
What Founders Say
No independently sourced founder testimonials found.
Connections
- Co-founder, Optimizely — with Pete Koomen (now a Group Partner at Y Combinator) 313
- Co-founder, Limitless — with Brett Bejcek 5
- Partner, Rebel Fund — Y Combinator alumni investing fund whose investing partners include Steve Huffman (Reddit), Daniel Kan (Cruise), Max Mullen (Instacart), Trip Adler (Scribd), Jonathan Hirsch (Paradigm), and Sebastian Mejia (Rappi) 10
- Obama 2008 campaign alum — served as Director of Analytics on Obama for America 2008 12
- a16z relationship — Rewind seed round led by David Ulevitch at Andreessen Horowitz 5
- NEA relationship — Rewind Series A led by New Enterprise Associates 6
- YC W10 alum — Optimizely went through Y Combinator’s Winter 2010 batch 3
Sources
-
Business of Software, “Dan Siroker, Director of Analytics for Obama’s First Presidential Campaign to speak at Business of Software Conference,” 2013, accessed May 2026. https://businessofsoftware.org/2013/06/dan-siroker-director-of-analytics-for-obamas-first-presidential-campaign-to-speak-at-business-of-software-conference/↩↩
-
CNN Money, “Optimizely aims to give Obama 2012 election a data edge,” April 23, 2012, accessed May 2026. https://money.cnn.com/2012/04/23/technology/startups/optimizely-election/index.htm↩↩
-
Y Combinator, “Q&A with Pete Koomen, Cofounder of Optimizely,” accessed May 2026. https://www.ycombinator.com/blog/qa-with-pete-koomen-cofounder-of-optimizely/↩↩↩↩
-
TechCrunch, “Optimizely acquired by content management company Episerver,” September 3, 2020, accessed May 2026. https://techcrunch.com/2020/09/03/episerver-acquires-optimizely/↩↩
-
Andreessen Horowitz, “Investing in Rewind,” November 1, 2022, accessed May 2026. https://a16z.com/announcement/investing-in-rewind/↩↩↩↩
-
The Information, “AI Startup Rewind Gets 170 Offers—and $350 Million Valuation in Unusual Fundraising,” 2023, accessed May 2026. https://www.theinformation.com/articles/ai-startup-rewind-gets-170-offers-and-350-million-valuation-in-unusual-fundraising↩↩
-
First Round Review, “AI Hot Takes and Unusual Twitter Fundraising Strategies with Dan Siroker (Rewind AI),” accessed May 2026. https://review.firstround.com/podcast/ai-hot-takes-and-unusual-twitter-fundraising-strategies-with-dan-siroker-rewind-ai/↩↩↩↩↩↩↩↩↩↩↩↩↩
-
Dan Siroker (@dsiroker) on X, “Introducing Limitless: a personalized AI powered by what you’ve seen, said, or heard,” April 2024, accessed May 2026. https://x.com/dsiroker/status/1779857843895599383↩
-
TechCrunch, “Meta acquires AI device startup Limitless,” December 5, 2025, accessed May 2026. https://techcrunch.com/2025/12/05/meta-acquires-ai-device-startup-limitless/↩
-
Rebel Fund, “Rebel Theorem 4.0 Outperforms Human VCs at 65% IRR,” accessed May 2026. https://www.rebelfund.vc/blog-posts/rebel-theorem-4-0-outperforms-human-vcs-65-percent-irr↩↩↩
-
Tracxn, “Dan Siroker — portfolio and founded companies,” accessed May 2026. https://tracxn.com/d/people/dan-siroker/__xaT1DJdJiOFLYVd2JTmo0yrTOwA4KFa8BZTmnMFibcQ↩↩↩↩↩↩↩↩↩↩
-
Crunchbase, “Dan Siroker — Co-Founder & CEO @ Limitless AI (formerly Rewind AI),” accessed May 2026. https://www.crunchbase.com/person/dan-siroker↩
-
Y Combinator, “Pete Koomen: YC Partner,” accessed May 2026. https://www.ycombinator.com/people/pete-koomen↩
-
Crunchbase, “Seed Round - Navattic,” seed round closed March 17, 2022, led by Canvas with participation from 645 Ventures, Y Combinator, Dan Siroker, and Ben Thompson, accessed May 2026. https://www.crunchbase.com/funding_round/navattic-seed–26a2d29↩