Here's the full rundown on both players:
Nick Bosa — Yes, he's on track for Week 1. Bosa tore his right ACL in September 2025 (his third career ACL tear), but the tear was clean with no meniscus damage, which speeds recovery. He's been doing field work at OTAs and per his page, he's "expected to be ready for Week 1 in Australia (Sept. 10, 2026) — approximately 11 months post-injury." The 49ers targeted a late July/early August return to full practice. (from the Nick Bosa page)
Mykel Williams — The wiki doesn't have a dedicated player page for him, but he's mentioned prominently on the 49ers team page and the DC Raheem Morris page as a fellow ACL recovery case alongside Bosa. The team page notes "If Nick Bosa and Mykel Williams return from ACL injuries for Week 1, depth becomes the team's biggest advantage" — so it's framed as an expectation, not a lock. The DC page adds that both Bosa and Williams "may still be rough around the edges after season-ending 2025 injuries." No detailed timeline is available in the wiki for Williams specifically.
Bottom line: Bosa looks very good for Week 1. Williams is expected to be in the mix but with more uncertainty. For fantasy purposes (IDP leagues), Bosa is the priority target given the clear timeline and his elite pass-rushing upside in Raheem Morris's aggressive new scheme.