It's a Futures Contract. Non of the money is guaranteed unless he makes the roster next season (does get any signing bonus, though that is often minimal). Future contracts are most often for the league minimum ($800,000 per year) - as is his. Jags will likely bring on others to compete with him for the back-up job. Signing now gives him the benefit of being with the team through all off-season programs.
More on Futures contracts:
https://www.profootballnetwork.com/nfl-futures-contract-e... /