You can get proficiency in every skill at 6th level.

[thoroughlyS]

Thanks to the new paradigm where your background gives you a bonus feat, you can get proficiency in all skills one level earlier than previously. In order to do so, you need to be playing in a Dragonlance campaign, a Planescape campaign, or a campaign that allows the backgrounds from Glory of the Giants. By taking a background that doesn't provide a specific bonus feat, you can grab the Skilled feat. You can also take any race/lineage that gives 2 skills (e.g. half-elf, kenku, dhampir). And by starting as a rogue, you wind up with 11 skills at 1st level (2 from race, 2 from background, 3 from Skilled, and 4 from rogue), and have expertise in 2 of them. At 2nd level, knowledge cleric gives two more (both with expertise to boot!). At 3rd, ranger grants 1 skill and canny gives expertise with 1 more. At 4th level, bard gives 1 skill. Two more levels in bard means that at 6th level, you can go lore bard for the final 3 skills AND expertise with 2 more skills. All told, that is proficiency with every skill, and expertise with 7.

[Lvl 2 Expert]

You'll also be playing a 4-way multiclass character, although to be fair you're essentially a half caster at this point with ranged options to cover for your low HP and a little bit of sneak attack to partly make up for not having second attack.

In practice just having more party members with skills is probably better, but yeah, cool optimization.

[RogueJK]

You can do it at Level 5 this way, eliminating the Ranger level:

Custom Lineage/Variant Human (1)
Eldritch Adept: Beguiling Influence feat at Level 1 (2)
Background (2)
Skilled feat from background (3)
Rogue 1 (4)
Knowledge Cleric 1 (2)
Lore Bard 3 (1+3)

That's proficiency in all 18 skills by Level 5 as a Rogue 1/Cleric 1/Bard 3.

I'd recommend continuing as a Soulknife Rogue from there, which would then allow you to utilize Psi-Bolstered Knack on any failed skill check, since you have proficiency in all skills. Ending up something like a Knowledge Cleric 1/Lore Bard 3/Soulknife Rogue X. You'd have proficiency in all skills, Expertise in 6 of the skills (eventually 8 after Rogue 6), and could add Guidance and Psi-Bolstered Knack on top, plus you can cast Enhance Ability for Advantage.



Also doable by Level 6 as a Scout Rogue 3/Lore Bard 3, if you want to minimize multiclassing (though this eliminates the Soulknife route):

Custom Lineage/Variant Human (1)
Eldritch Adept: Beguiling Influence feat at Level 1 (2)
Background (2)
Skilled feat from background (3)
Scout Rogue 3 (4+2)
Lore Bard 3 (1+3)

[Amnestic]

You can do it at Level 5 this way, eliminating the Ranger level:


You can't take Eldritch Adept at 1 if your first level is Rogue - the feat requires the Spellcasting or Pact Magic features.

[RogueJK]

Good catch. So we're back to Level 6, but you can still do it without the Ranger level as a Rogue 1/Knowledge Cleric 1/Lore Bard 4, and you'll end up with an extra +1 stat bump and an additional caster level too:

Race with 2 racial skills (2)
Background (2)
Skilled feat from background (3)
Rogue 1 (4)
Knowledge Cleric 1 (2)
Lore Bard 4 (1+3)
Skill Expert at Bard 4 (1)

Also doable without Bard as a Scout Rogue 4/Ranger 1/Knowledge Cleric 1, provided you take Rogue 4 after Cleric 1:

Race (2)
Background (2)
Skilled feat from background (3)
Scout Rogue 4 (4+2)
Eldritch Adept Beguiling Influence at Rogue 4 (2)
Ranger 1 (1)
Knowledge Cleric 1 (2)

[thoroughlyS]

I think Rogue 1/Knowledge Cleric 1/ Lore Bard 4+ taking Skill Expert is the way to go. Two levels of dips and a half-feat is a common amount of investment, and the wait to 18 CHA isn't too bad. Sure, Jack of All Trades becomes redundant, but I think it's worth not having to eat Eldritch Adept for the last two skills.

[thoroughlyS]

Well now I feel silly. It has been pointed out to me that this was already possible since TCoE. Variant human/custom lineage taking Skilled is only one skill down at 1st level, and you can just take Eldritch Adept at 6th level instead of Skill Expert. You miss out on 18 CHA and one expertise, but it is the same level.

[Yakmala]

For those who want to get most of the skills as early as Tier 1, I suggest a Half Elf Knowledge Cleric 1, Scout Rogue 3. By Level 4, you'll have 15 of 18 skills and 6 expertise.

Proficiency:
Half Elf (2)
Background (2)
Skilled Background Feat (3)
Rogue (4)
Scout (2)
Knowledge (2)

Expertise:
Rogue (2)
Scout (2)
Knowledge (2)